Hi!
I would like the option to over clock my RPi 4. The latest firmware allows (from what I understand)over clocking up to 2000 MHz. Currently the options under “performance” doesnt allow this for RPi 4.

You guys might run some tests, which combinations of arm_freq, core_freq and overvoltage lead to a stable system.
AFAIK sdram_freq has no effect on RPi4, it's fix 3200. At least reading through some overclocking threads on the RPi forums it was never used, and checking it's value (vcgencmd get_config sdram_freq) always returns zero.

Works wonders and is 100% rock stable after 6 hours of stress testing. It seems nearly _all_ devices can hit that if the RPi4 is cooled actively. The RPi4 is a hot one, so DietPi should probably show a warning that active cooling is recommended, or the CPU will throttle easily.

People are reporting arm_freq=2000 is possible with over_voltage=4, but not all CPU can handle it (most can, but in the CPU-lottery you never know..). There is a risk the RPi won't boot at those freqencies and require the user to manually edit the config.txt on a different system to restore the system.

My second RPi4 just arrived so I'm going to do some testing, and probably get a stable system at 2000 mhz. I'll report back then.

So one can choose to speed up either GPU-loading or ARM-loading tasks a bid more. Sets that run stable with over_voltage=6 should be the maximum, since AFAIK a higher values still voids guarantee and requires force_turbo=1.

@aftensleuk
Nice, thanks again for sharing. Okay so 2000/500 seems to work with over_voltage=4 at least in most cases. However, I will go through the raspberrypi.org forum before adding this, probably we use over_voltage=5 to be failsafe?

Yes, I think I was just lucky. I don't think 2000 mhz with over_voltage=4 should be general. From what I see on different forums a higher over_voltage is needed in some cases for being able to run a 6 hour stress test.

However, the reason I even tried over_voltage=4 instead of 6 is that with over_voltage=6, not even the fan shim would be sufficient. The temps hit 73-74 degrees when doing DietPi:s stress test (CPU was throttling a bit). When I lowered to over_voltage=4, temps are between 68-70 degrees during stress test and no thermal throttling occurred. As to what the Dietpi-overcloking profiles should look like; With over_voltage=4 it would be better to set the cpu to 1850-1900 mhz, rather than trying to raise the voltage and get even higher speeds considering not even a fan shim is enough for over_voltage=6.

There should definitely be a disclaimer with RPi4 that active cooling is highly recommended before using the overclocking profiles.

@aftensleuk
Definitely makes sense to warn user and recommend to monitor temperatures in idle and during stress test to verify that cooling is sufficient. Overclocking is of course useless if temp raise to limit and force throttling.

Perhaps we should not offer >4 overvoltate profiles then. The profiles we offer should be safe in usual environments. If your fan does not bring down +6 voltage temps below 70°C during stress test, then this IMO is no usually reasonable profile. Probably this:

@MichaIng
In the over clocking scene there's usually people who wants to do inverted over clocking. Meaning they want the same performance but with less generated heat.

Therefore I tried under clocking my machines too:

over_voltage=-2 (read minus 2!) @ 1500 mhz arm cpu. It does run cool and energy efficient so far and seemingly very stable under normal use conditions. According to documentation a negative over_voltage value is possible, so I think it'd be a good idea to introduce that feature too for those trying to control the heat of the very hot RPi4.

However, there's not much information posted on forums about other people doing under clocks so I'm not sure how stable it is to generally do that. It does work fine on two of my RPi machines though (I have only stress tested them for 5 minutes each).

@aftensleuk
Makes sense actually, especially for headless devices where the GPU has not much to do.
I read some week(s) ago that undervoltage (negative values) did not work on RPi4, but it seems then that this issue has been fixed with latest firmware.